How do I choose the next item after using Autocomplete in the Python Console?
The autocomplete functionality relies on uniqueness.

So bpy.ctrl+space
lists all the objects in the bpy name space.

And bpy.octrl+space
results in the single value ops as nothing else starts with o

When the match is ambiguous e.g. bpy.pctrl+space
you get two results

ath
rops


(for path and props)

There is no way to use keyboard shortcuts to select the correct entry, but if you double click on the item you want the entire item will be selected and then you can copy and paste ctrl+c, ctrl+v.

Remember Blender is open source, so in theory you could submit a patch that would add additional functionality to the Python console.